A machine tool is provided with a clamp device for removably mounting the tool holder holding a tool, in a hollow spindle of the spindle device. During a working operation, the tool holder and the tool are rotated at high speed in conjunction with the rotation of the spindle.
Such a clamp device typically has a configuration where a clamp sleeve is attached to a distal end of a draw-in bolt which is axially reciprocated, while a distal end of the clamp sleeve is opened or closed according to the positional shift of the clamp sleeve with reciprocation of the draw-in bolt relative to a spindle body as an outer sleeve defining an outer periphery of the clamp sleeve. In an open state of the clamp sleeve, a tip of a pull-stud bolt of the tool holder is inserted in the clamp sleeve, then, in a closed state of the clamp sleeve, the pull-stud bolt is clamped in place.
As shown in FIG. 2, for example, a specific configuration of the clamp device is such that a clamp sleeve 105 slidably disposed in an interior space 103 of a hollow spindle body 104 constituting a spindle 102 is formed with a plurality of through-holes 106 on a circumference of a front end thereof at equal angular spaces, and steel balls 107 are fitted in the respective through-holes 106. The spindle body 104 includes in its bore region corresponding to the clamp sleeve 105: the bore region of the spindle body is formed with: a forward small diameter portion 104a conformable to an outside diameter of the clamp sleeve 105; and a large diameter portion 104b diametrally expanded from the forward small diameter portion.
In this clamp device 101, the clamp sleeve 105 is normally biased rearward by an elastic force of a coned disc spring 110. A drive mechanism for pushing forward a draw-in bolt 108 against the biasing force of the coned disc spring 110 is disposed at a rear end of the draw-in bolt 108.
In the case of the clamp device shown in FIG. 2, a piston rod 21 of a hydraulic cylinder 20 is coupled to the rear end of the draw-in bolt 108. When mounting a tool holder 30, therefore, the hydraulic cylinder 20 drives so as to advance the draw-in bolt forward, so that the coned disc spring 110 is flexed to push forward the clamp sleeve 105. This movement brings a region of the through-holes 106 to the forward large diameter portion 104b in the spindle body 104, establishing an unclamp state that allow the steel balls 107 in the through-holes to move outward. In this unclamp state, when a head 32 of a pull-stud bolt 31 connected to a tip of the tool holder 30 is inserted in the clamp sleeve 105 from a distal end thereof, the head 32 can pass through the inside of the clamp sleeve as pushing outward the steel balls 107.
When the hydraulic cylinder 20 stops pushing forward the draw-in bolt 108 after the insertion of the pull-stud bolt 31, the coned disc spring 110 restores the biasing force which pushes the draw-in bolt 108 rearward. Accordingly, the clamp sleeve 105 is also pulled rearward. This movement brings the region of the through-holes 106 to the forward small diameter portion 104a in the spindle body 104, while the steel balls 107 in the through-holes are pushed inward to be engaged with a neck under the head of the pull-stud bolt 31 and to clamp the pull-stud bolt. Thus is established a clamp state.
In addition to the above steel-ball type clamp portion, the clamp device also adopts a collet chuck type, for example. As disclosed in Patent Literature 1 and Patent Literature 2, this type of clamp device establishes the unclamp state and the clamp state by opening or closing a distal end of a collet, having an outside configuration in which a cylindrical body diametrally expanding in a tapered fashion and is formed with slits radially extended from the center thereof.
Specifically, the collet chuck type has a mechanism where the collet is displaced to the large diameter portion of the outer sleeve on the outside by being pushed forward by the draw-in bolt at the rear end against the biasing force of the coned disc spring, so that the distal end of the collet is opened to be placed in the unclamp state. And when the collet is pulled rearward by the biasing force of the coned disc spring in conjunction with the rearward movement of the draw-in bolt, the collet is displaced to the small diameter portion of the outer sleeve, so that the distal end of the collet is closed as externally clamped by an inside surface of the outer sleeve, thus the collet holding the head of the pull-stud bolt.